Please keep in mind that performing anything suggested in this instructable is at your own risk. If you have no experience with a dremel, practice, this project is potentially dangerous if not approached properly.
Now that the disclaimer is out of the way, let's get started.
This instructable is for anyone looking to get a bit more performance out of their car and learn a bit more about their car in the process. The basic principle behind modifying a car is to have more air/fuel enter the combustion chamber. The port and polish basically makes it easier for air/fuel to flow into the combustion chamber and gasket matching permits a greater volume. (more gas and air equals bigger/more powerful explosion equals more torque and horsepower)
Keep in mind that this is a very large project. I have put over 20 working hours into my sunfire's head.
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Step 1: Gather Materials and Tools
For this you will need:
1 or 2 heads (car dependent)
Various sanding bits for the dremel
Face mask (inhaling metal shavings is no fun)
High Accuracy measuring device (optional and preferable for those who intend to get really serious with this project)
Step 2: Examine the Head(s)
Every car will be different, the head pictured came from a 98 Sunfire (Engine LN2). Make note of any manufacturing defects. Usually the better-defined bumps are intentional for fuel atomization. On the sunfire's head, there was a mold ring (left over from the casting process). We will start by removing any defects.
Step 3: Begin Grinding
DO NOT grind away the topmost lip, this is the seat for the valve and damage will cause leakage. Use a lower grit sander to start on moderate speed. Slowly shave the excess metal off until the port is smooth. Do not rush this, it's greatly preferable to spend weeks on this than destroy the head and have to buy another.
Step 4: Gasket Matching
Align the exhaust and intake gaskets one at a time and mark how much of each port is to be removed. Leave 1 to 2mm of metal between the gasket and the holes. Once finished with this it's time for polishing.
Step 5: Polishing
Now it's time to swap out that low grit dremel bit for a high grit one. Go over the entirety of the ports until they near a mirror shine. Once finished you can have the head decked and pressure-checked by a professional.
Step 6: Conclusion
And that's it, install the head on the car and enjoy the power boost. Of course like all car modifications the increase will be dependent on the rest of the car (what other performance parts are installed). The LN2 specifically has a lot to gain from a gasket match and port/polish because of lower manufacturing standards.
This is my first instructable and constructive criticism is more than welcome. I look forward to prototyping some of my ideas and posting them.